This invention relates to a power supply device including a unbalance monitoring circuit for a direct voltage transmitted between two line conductors, and which is balanced with respect to ground potential.
In optical communication transmission systems, two metallic line conductors are provided in parallel with the fibre glass lines transmitting the communication signals. The metallic line conductors supply a direct voltage, generated by a power supply device, to the line devices of the transmission link, for example, amplifiers (power feeding). For this purpose, the first line conductor is connected to the pole of the direct voltage which is positive with respect to ground potential and the second line conductor is connected to the pole which is negative with respect to the ground potential. The amplitude of the potential existing at the positive pole corresponds to the amplitude of the potential occurring at the negative pole. Thus, a direct voltage is present between the two line conductors which is balanced with respect to ground potential. The line devices connected to the transmission system are grounded in each case. If a line conductor is damaged, for example, due to digging work, and, as a result, this line conductor is connected to the ground potential (unilateral ground fault), this unbalance of the direct voltage results in a disturbance or a failure of the line devices that are energized by the direct voltage. The purpose of an unbalance monitoring circuit is to monitor this operating condition.